Fecal, or stool samples are routinely tested for the presence of viruses, bacteria, parasites, other organisms, and antigens shed from such organisms. Methods for conducting such assays begin with stool collection, usually involve a number of fecal sample manipulation steps and typically end with the development of a signal such as color formation within a signal development means to indicate the presence or absence of a test analyte.
Stool collection is usually non-invasive and is ideal for obtaining samples of certain digestive disease organisms such as salmonella and cholera. Stool can be collected with a swab during examination and applied directly to a test surface or volume.
Traditional fecal examinations have used complex chemical and microbiological methods. These methods are being replaced with immunoassay methods. Immunoassay methods are highly sensitive and require only a small sample. Some immunoassay methods such as latex agglutination and enzyme immunoassays can be performed with test kits that contain vials and reagent solutions that are combined in a particular way to obtain a test result.
Although many immunoassay methods do not require electronic instrumentation or university trained clinicians for their use, they are not easily carried out in underdeveloped areas of the world where modern devices and techniques are poorly understood. Even the simplest immunoassays usually require timed addition of reagents to test samples and the manipulation of plastic test parts that have to be brought together in a proper order.
The application of immunoassay techniques to fecal analysis in particular is difficult for several reasons. Stool handling is disagreeable and hazardous. Sanitary and inoffensive procedures for processing stool are awkward and often complex. Such procedures may include weighing, centrifuging and storing, and are difficult except in a clinical laboratory equipped with a suitable apparatus, protective equipment, and a skilled technician.
However, stool samples have to be processed before their use in an immunoassay in order to remove interferences. This processing can cause complexity within the test method and prevents more widespread use of cholera tests in rural and lesser developed regions where machinery and reagents for processing are nonexistent.
Any reduction in the number of steps required to perform a fecal test and any reduction in contact between test operator and the test material could be a boon to testing in this area, particularly where a lethal disease agent such as cholera is involved. Such an advance would directly advance health by allowing earlier and more complete testing of cholera.
Attempts have been made to alleviate the methodology problem of handling stool specimens. For example, M. A. Grow et al. in U.S. Pat. No. 5,198,365 describe a fecal sample handling method for a hemoglobin immunoassay that requires dilution of a stool specimen by 10 to 100 fold. Although dilution possibly can simplify the assay procedure, it lowers sensitivity by a dilution factor. A 10 to 100 fold dilution step is particularly unacceptable for many tests of infectious agents such as cholera because greater test sensitivity is desired to detect these agents at earliest clinical time periods.
On the other hand, if a sample is tested without a significant dilution (i.e. more than 3 fold) then a centrifugation and/or filtering step is generally required as described by Vellacott et al., Lancet (Jan. 3, 1981) and by Jikunen et al. in the Scand. J. Infect. Dis. 17: 245 (1985).
A recent attempt to eliminate the complexity problem in testing stool specimens was described in J. Clin. Micro. 32: 249 (1994) by J. A. K. Hasan et al. This reference cites a rapid calorimetric immunodiagnostic kit for the detection of the presence of Vibrio cholera 01 in clinical specimens.
In the procedure a stool specimen is passed through a filter that is separate from other kit components. Four drops of the stool filtrate are added to two drops of reconstituted gold labeled anti-vibrio cholera antibody. A swab is first added to the solution and then placed in an immunoassay testing device. Within the device, formed immune complexes are captured on a porous membrane that contains immobilized anti-vibrio cholera antibody.
Unfortunately, the separate filtration step in this procedure prolongs the test. The test is too complex for many untrained people and requires separate manipulation of two vials, one vial cap, a swab and an immunoassay device. Furthermore, test kits and methods that require many manipulations have more sources of error which lead to higher error rates. Finally, manufacturing costs increase when multiple parts and separate reagents are added to test kits.
Thus, there exists a need for simpler and safer fecal test devices.